Superheated steam generator and maintenance method therefor

ABSTRACT

The present invention is intended to inform a user of a maintenance timing for a superheated steam generator. The present invention includes an induction heating type or electrically heating type superheated steam generation section and an informing section. The superheated steam generation section generates superheated steam by heating steam. The informing section transmits maintenance information by employing, as a parameter, an operating temperature of the superheated steam generation section and an operating time at the operating temperature.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a superheated steam generator and amaintenance method therefor.

Background Art

Austenitic stainless steels such as SUS304, and alloys such as INCONEL(registered trademark), each of which has high heat resistance and highmechanical proof stress, are used for an induction heating type orelectrical heating type superheated steam generation section (forexample, Patent Document 1).

However, even though these stainless steels and alloys have a meltingpoint of approximately 1400° C., volume reduction may occur due to steamoxidation in superheated steam having high temperatures exceeding 1000°C.

The above superheated steam generation section includes a conductor tubecomposed of stainless steel or alloy. Therefore, when the volumereduction occurs due to the steam oxidation, the conductor tube cannotwithstand the pressure of the superheated steam and deformation due tothermal expansion, thus causing damage to the conductor tube. Thesuperheated steam may leak outside due to the damage to the conductortube. This may cause, for example, fire and personal injury.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Unexamined Patent Publication No.2016-176613

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Accordingly, the present invention has been made to solve the aboveproblem and has for its main object to inform a user of a maintenancetiming for a superheated steam generator.

Means of Solving the Problems

In one embodiment, a superheated steam generator includes an inductionheating type or electrically heating type superheated steam generationsection, and an informing section. The superheated steam generationsection is configured to generate superheated steam by heating steam.The informing section is configured to transmit maintenance informationby employing, as a parameter, an operating temperature of thesuperheated steam generation section and an operating time at theoperating temperature.

With the above configuration, the maintenance information is transmittedby employing the operating time at the operating temperature as aparameter. It is therefore possible to inform a user of a maintenancetiming for the superheated steam generator. This makes it possible forthe user to carry out maintenance before the superheated steamgeneration section breaks down.

Degrees of deterioration and fatigue of the superheated steam generationsection differ depending on an operating temperature. Hence, preferably,the informing section acquires operating temperature data indicating theoperating temperature of the superheated steam generation section, andoperating time data indicating the operating time at the operatingtemperature. The informing section then converts the operating time tothe operating time at a predetermined temperature (for example, 1200°C.) and integrates converted values. Subsequently, the informing sectiontransmits the maintenance information when an integration value exceedsa predetermined integration threshold value.

The superheated steam generator may include a conductor tube to generatethe superheated steam by being subjected to induction heating orelectrical heating, and a steam adjustment mechanism for adjusting anamount of superheated steam to be generated. A flow rate of thesuperheated steam in the conductor tube is increased or decreaseddepending on whether the amount of superheated steam generationincreases or decreases. A high flow rate leads to a great volumereduction rate, and a low flow rate leads to a small volume reductionrate.

Because a volume reduction rate is proportional to a flow rate to thepower of 0.8 in actual measurements at 1200° C., a flow rate is halvedwhen the amount of superheated steam generation is halved, and acorrected integration value (operating time) reaches a value of0.5^(0.8)=0.574 times with respect to an integration value beforecorrection. In other words, assuming that the superheated steamgenerator is operated for 1000 hours at an amount of generation of 100%in the case of generating superheated steam at the same temperature, theoperating time reaches 574 hours by operating at an amount of generationof 50%.

Thus, the volume reduction rate differs depending on the amount ofsuperheated steam. Hence, preferably, the informing section corrects theintegration value on a basis of an amount of superheated steamgeneration in the superheated steam generation section, and theinforming section transmits the maintenance information when a correctedintegration value exceeds the integration threshold value.

The superheated steam generation section includes a conductor tube togenerate the superheated steam by being subjected to induction heatingor electrical heating. The conductor tube is susceptible to steamoxidation due to the superheated steam, and the volume reduction isremarkable. Therefore, the informing section is preferably configured totransmit the maintenance information containing a replacement timing forthe conductor tube.

The useful lifespan is less likely to become a problem even withoutconsideration of the operating time in a range of temperatures at whicha volume reduction due to steam oxidation does not substantially becomea problem. For example, when the superheated steam at 1000° C. is passedthrough a conductor tube composed of INCONEL for 1000 hours, a volumereduction rate is approximately 5%. In other words, it takes severaltens of thousands of hours at 1000° C. or below until a remaining amountof a flow tube is reduced to 10% or less. It is therefore less likelythat the useful lifespan will become a problem in a short period oftime. Hence, the informing section is preferably configured to transmitthe maintenance information by employing, as a parameter, an operatingtemperature at which the volume reduction rate of the flow tube reachesor exceeds a predetermined value by operating for a predetermined periodof time. The informing section also preferably specifies a temperaturerange used for the maintenance information at the operating temperaturesof the superheated steam generation section, and utilizes the operatingtime at the operating temperatures included in the temperature range, asthe operating time at a highest temperature in the temperature range.

It is conceivable to include a first superheated steam generationsection of the induction heating type and a second superheated steamgeneration section of the electrically heating type, as a specificconfiguration of the superheated steam generation section. The firstsuperheated steam generation section carries out induction heating byusing, as a secondary coil, a first conductor tube that permits passageof steam. The second superheated steam generation section further heatsthe superheated steam by electrically heating a second conductor tubethat permits passage of superheated steam generated by the firstsuperheated steam generation section.

A use method is conceivable which accelerates fatigue of the secondconductor tube by setting a higher temperature to the second superheatedsteam generation section than the first superheated steam generationsection in the above configuration. Here, it is preferable that theinforming section is disposed at a side of the second superheated steamgeneration section and is configured to transmit the maintenanceinformation indicating a replacement timing for the second conductortube.

More preferably, the informing section is also disposed at a side of thefirst superheated steam generation section so as to transmit themaintenance information indicating the replacement timing of a conductortube of the first superheated steam generation section. This makes itpossible to also inform the user of the maintenance timing for the firstsuperheated steam generation section aside from the second superheatedsteam generation section. Here, a maintenance frequency for replacementof the second conductor tube or the like in the second superheated steamgeneration section is higher than the maintenance frequency ofreplacement of the first conductor tube or the like in the firstsuperheated steam generation section.

Because the first conductor tube is wound around an iron core in thefirst superheated steam generation section of induction heating type,disassembly for replacing the conductor tube is complicated andtime-consuming. It is therefore difficult to carry out maintenance, suchas replacement of the first conductor tube. In contrast, it is easy tocarry out maintenance, such as replacement, by a simple operation, suchas removal of power source wiring from power supply terminals of thesecond conductor tube, in the second superheated steam generationsection of electrically heating type. Consequently, the firstsuperheated steam generation section is used under service conditions(for example, at below 1000° C.) under which the conductor tube is lesslikely to deteriorate or fatigue, thereby minimizing the frequency ofmaintenance, such as replacement. The second superheated steamgeneration section is configured to generate the superheated steamhaving high temperatures (for example, 1000° C. or higher) because it iseasy to carry out maintenance for replacement of the second conductortube.

Effects of the Invention

With the present invention configured as described above, themaintenance information is transmitted by employing, as a parameter, theoperating time at the operating temperature. It is therefore possible toinform a user of maintenance timing for the superheated steam generator.This makes it possible for the user to carry out maintenance before thesuperheated steam generation section breaks down.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a configuration of asuperheated steam generator in one embodiment;

FIG. 2 is a perspective view illustrating one embodiment of a conductortube of a superheated steam generation section in the embodiment;

FIG. 3 is a diagram illustrating superheated steam-INCONEL 601 alloyvolume reduction characteristics after 1000 hours; and

FIG. 4 is a diagram schematically illustrating a configuration of asuperheated steam generator in a modified embodiment.

MODE FOR CARRYING OUT THE INVENTION

One embodiment of a superheated steam generator according to the presentinvention is described below with reference to the drawings.

As illustrated in FIG. 1, a superheated steam generator 100 in thepresent embodiment includes a superheated steam generation section 10configured to generate superheated steam exceeding 100° C. (e.g.,200-2000° C.) by heating water or steam.

The superheated steam generation section 10 employs induction heating,and includes a spiral-wound circular tube-shaped conductor tube 2 and amagnetic flux generation mechanism 3 by which the conductor tube 2 issubjected to induction heating.

As illustrated in FIG. 2, the conductor tube 2 is composed of a metaltube, and includes a winding part being wound spirally. One end of theconductor tube 2 is provided with an inlet port P1 that permitsintroduction of water or steam, and the other end is provided with anoutlet port P2 that permits discharge of generated superheated steam.Austenitic stainless steels such as SUS304, and alloys such as INCONEL,each of which has a high heat resistance and high mechanical proofstress, is usable for the conductor tube 2.

External piping for supplying water or steam to the conductor tube 2 iscoupled to the inlet port P1. Specifically, an induction heating typesaturated steam generation section (not illustrated) is coupled to theinlet port P1 in the present embodiment. The saturated steam generationsection has the same configuration as the superheated steam generationsection 10. External piping for supplying generated superheated steam toa use-side (for example, a heat treatment chamber) is coupled to theoutlet port P2.

The magnetic flux generation mechanism 3 includes an iron core 31 and aninduction coil 32 wound along the iron core 31. An alternating current(AC) power source 4 is coupled to the induction coil 32 so as to supplycontrolled power thereto. A power source frequency of the AC powersource 4 is a commercial frequency of 50 Hz or 60 Hz. The induction coil32, to which the power is supplied from the AC power source 4, serves asa primary coil. By supplying power through the primary coil, an inducedcurrent flows to the conductor tube 2, and the conductor tube 2 servesas a secondary coil. The conductor tube 2 is subjected to Joule heating,so that steam passing through the interior of the conductor tube 2 canbe heated.

With the superheated steam generator 100, an AC voltage applied to theinduction coil 32 is controlled by detecting through a temperaturedetector 5 a temperature of superheated steam discharged from theconductor tube 2, and by inputting a control signal according to adeviation between a detected temperature and a target temperature, to avoltage controller 6 (for example, a thyristor). Specifically, atemperature controller 7 configured to perform the above controlperforms a feedback control of the temperature of the superheated steamheated through the conductor tube 2 so that a deviation from the targettemperature is less than ±1° C. The temperature controller 7 is acomputer including, for example, a central processing unit (CPU),memory, and an input/output interface.

The superheated steam generator 100 of the present embodiment furtherincludes an informing section 8 configured to transmit maintenanceinformation by employing, as a parameter, an operating temperature ofthe superheated steam generation section 10, an operating time at theoperating temperature, and a volume reduction rate at the operatingtemperature.

The informing section 8 acquires operating temperature data indicatingthe operating temperature of the superheated steam generation section10, and operating time data indicating the operating time at theoperating temperature. The informing section 8 then converts this datato the operating time at a predetermined temperature and integratesconverted values. The informing section 8 transmits the maintenanceinformation when an integration value exceeds a predeterminedintegration threshold value. The informing section 8 is a computerincluding, for example, a processor such as a central processing unit(CPU), memory, and an input/output interface.

Specifically, the informing section 8 employs, as operating temperaturedata, detected temperature data indicating a detected temperatureobtained through the temperature detector 5, or target temperature dataindicating a target temperature controlled by the temperature controller7. The informing section 8 acquires the operating time data indicatingoperating time from a timer included in the informing section 8, or atimer of the temperature controller 7. The informing section 8 convertsthis data to the operating time at 1200° C. and integrates the convertedvalues. The informing section 8 transmits maintenance information whenthe integration value exceeds a predetermined integration thresholdvalue. Alternatively, temperatures of the conductor tube 2 may be usedas the operating temperature data. In this case, a temperature detectoris contactedly disposed, for example, at the outlet port P2 of theconductor tube 2 or in the vicinity thereof. Particularly, when thesuperheated steam generation section 10 is in a standby state orperforms an intermittent operation, it is preferable to use thetemperatures of the conductor tube 2.

The predetermined integration threshold value corresponds to a volumereduction limit time, and needs to be determined by previouslycalculating from a pressure of superheated steam and a thermal expansiondeformation value of the conductor tube 2. An approximation formula of arelationship between volume reduction rate and temperature needs to beobtained by carrying out measurements at several points (refer to FIG.3). Using a detected temperature obtained through the temperaturedetector 5 or a target temperature controlled by the temperaturecontroller 7, a volume reduction rate is calculable from the detectedtemperature or the target temperature.

A test operation for each type of superheated steam generator is carriedout at a highest temperature until the conductor tube 2 breaks down.This is because fracture conditions differ depending on a curvature ofthe conductor tube 2, the flow rate of the superheated steam, and theamount of superheated steam generation.

A fracture test was conducted by using a model having, for example, anamount of superheated steam generation of 60 kg/h and a capacity forgenerating superheated steam at 1200° C., and by using a conductor tubecomposed of INCONEL (with an outer diameter of ϕ 33.4 mm, an innerdiameter of ϕ 26.64 mm, and a tube thickness t of 3.38 mm). A remainingwall thickness of a fractured highest-temperature part was 0.45 mm.Volume reduction rate characteristics after 1000 hours are presented inFIG. 3, and a reduction rate is given by equation “y.”

When operated for 1000 hours at the superheated steam temperature of1200° C., a tube thickness t is 1.4872 mm (a reduction rate y₁₂₀₀=0.56),resulting in a reduction of 1.8928 mm.

When a usable limit is set to 0.5 mm, a tube thickness reduction valueis 3.38-0.5=2.88 mm. Reach time T is as follows:T=2.88/(1.8928/1000)≈1521 hours.

When set to a reduction rate y₀ for an operating time h₀ at an operatingtemperature θ, a converted operating time h₁₂₀₀ at 1200° C. ish₁₂₀₀=y₀×h₀/y₁₂₀₀.

In cases where the operating time at each temperatures is, for example,500 hours at 1200° C., 500 hours at 1100° C., and 500 hours at 1000° C.,the converted operating time at 1200° C. is as follows.

Converted operating time h ₁₂₀₀=500+(0.33/0.56)×500+(0.05/0.56)×500≈840hours

The maintenance information, such as an alarm sound, indicating areplacement timing for the conductor tube 2 is transmitted when theabove converted operating time reaches a predetermined integrationthreshold value.

The transmission of the maintenance information includes, for example,displaying a warning on a display, outputting the alarm sound from aspeaker, and turning on or flashing a lamp, such as a light emittingdiode (LED). Alternatively, the predetermined integration thresholdvalue may be set in multiple stages, and the maintenance information maybe transmitted stepwise according to the converted operating time.Furthermore, the time remaining until reaching the volume reductionlimit time may be displayed on the display.

With the superheated steam generator 100 so configured, the maintenanceinformation is transmitted by employing, as a parameter, the operatingtime at the operating temperature. It is therefore possible to inform auser of the maintenance timing for the superheated steam generator 100.This makes it possible for the user to carry out maintenance before, forexample, the conductor tube 2 of the superheated steam generator 100breaks down.

The present invention is not limited to the above embodiment.

For example, as a value calculated in order that the informing section 8transmits the maintenance information, an integration value of a productof the operating time at the operating temperature multiplied by thevolume reduction rate at the operating temperature may be used insteadof the converted operating time in the above embodiment.

Alternatively, the informing section 8 may transmit the maintenanceinformation by taking into consideration only an operating temperatureat which the volume reduction substantially becomes a problem.Specifically, the informing section 8 transmits the maintenanceinformation by employing, as a parameter, the operating temperature atwhich a volume reduction rate of the conductor tube 2 reaches or exceedsa predetermined value (for example, 5%) by operating for a predeterminedperiod of time. For example, the informing section 8 integrates theoperating time at or above an operating temperature (1000° C. forINCONEL) at which the volume reduction rate of the conductor tube 2reaches, for example, 5% by operating, for example, for 1000 hours. Theinforming section 8 transmits maintenance information, for example, whenan obtained integration value exceeds a predetermined integrationthreshold value.

The informing section 8 may specify a temperature range used for themaintenance information in the operating temperatures of the superheatedsteam generator 10, and may utilize the operating time at the operatingtemperatures included in the temperature range, as the operating time ata highest temperature in the temperature range. For example, temperatureranges used for the maintenance information may be specified as900-1000° C., 1000-1100° C., and 1100-1200° C. The informing section 8utilizes the operating time in the range of 900−1000° C. as theoperating time at 1000° C., and accumulates as the operating time at1000° C. Similarly, the informing section 8 utilizes the operating timein the range of 1000−1100° C. as the operating time at 1100° C., and theoperating time in the range of 1100−1200° C. as operating time at 1200°C.

The temperature controller 7 may cause the superheated steam generationsection 10 to stop operation by acquiring a signal indicating that theinforming section 8 has transmitted the maintenance information. Thetemperature controller 7 and the informing section 8 may be configuredwith an identical computer.

Although the above embodiment is configured to transmit the maintenanceinformation indicating the replacement timing for the conductor tube 2,the above embodiment may be configured to transmit the maintenanceinformation indicating the replacement timing for external pipingcoupled to the outlet port P2 of the conductor tube 2.

The informing section may employ, as a parameter used for themaintenance information, the flow rate of superheated steam flowingthrough the conductor tube 2, and the amount of superheated steamgeneration. For example, the informing section may correct anintegration value on the basis of the amount of superheated steam in thesuperheated steam generation section. The informing section transmitsthe maintenance information when a corrected integration value exceedsan integration threshold value. When the amount of superheated steamgeneration is employed as a parameter, the informing section may beconfigured to increase or decrease the operating time by using an amountof adjustment obtained through a steam adjustment mechanism or ameasurement value obtained through a measuring section for measuring theamount of superheated steam generation. When the amount of generation isgreater than a predetermined amount of superheated steam generation, itis conceivable to increase the operating time accordingly. When theamount of generation is smaller than the predetermined amount ofsuperheated steam generation, it is conceivable to decrease theoperating time accordingly. Here, the informing section corrects theoperating time (an integration value) by using a relationship betweenthe volume reduction rate and flow rate at each temperature (a volumereduction rate is proportional to 0.8 times a flow rate at 1200° C.).

Alternatively, the informing section may be configured to transmit themaintenance information by employing a wall thickness of the conductortube 2 as a parameter.

The superheated steam generation section 10 may be of the electricallyheating type instead of the induction heating type. In this case, theconductor tube 2 is subjected to Joule heating by coupling an AC powersource or a direct current (DC) power source to both end portions of theconductor tube 2 that permits passage of fluid, and by passing an ACcurrent or a DC current through the conductor tube 2.

Alternatively, a superheated steam generator may be one which isobtained by combining the induction heating type and the electricallyheating type as illustrated in FIG. 4. Specifically, the superheatedsteam generation section 10 includes a first superheated steamgeneration section 10A of the induction heating type configured to carryout induction heating by using, as a secondary coil, a conductor tubethat permits passage of steam, and a second superheated steam generationsection 10B of the electrically heating type configured to further heatthe superheated steam by electrically heating the conductor tube thatpermits passage of the superheated steam generated by the firstsuperheated steam generation section 10A.

The first superheated steam generation section 10A has the sameconfiguration as that in the above embodiment. The first superheatedsteam generation section 10A is configured to generate superheated steamat less than 1000° C. The second superheated steam generation section10B includes a conductor tube 11 coupled directly or through anintermediate pipe to the outlet port P2 of the conductor tube 2 in thefirst superheated steam generation section 10A. The conductor tube 11 isprovided with a plurality of nozzles 11 a for spraying superheatedsteam. Power supply terminals 12 and 13 are respectively disposed atboth end portions of the conductor tube 11, and an AC power source 17 iscoupled to these power supply terminals. A current flows through theconductor tube 11 by the AC power source, and therefore the conductortube is subjected to Joule heating, so that the superheated steampassing therethrough can be heated.

With the above superheated steam generator 100, an AC voltage applied tothe induction coil 32 is controllable by detecting through a temperaturedetector 14 a temperature of superheated steam discharged from theconductor tube 11, and by inputting a control signal according to adeviation between a detected temperature and a target temperature to avoltage controller 15 (for example, a thyristor). Specifically, thetemperature controller 16 configured to perform the above controlperforms the feedback control of the temperature of the superheatedsteam heated through the conductor tube 11 so that a deviation from thetarget temperature is less than ±1° C. The temperature controller 16 isa computer including, for example, a processor such as a CPU, memory,and an input/output interface.

The informing section 8 is disposed on a side of the second superheatedsteam generation section 10B. Detected temperature data indicatingdetected temperatures obtained through the temperature detector 14 ortarget temperature data indicating a target temperature controlled bythe temperature controller 16 are used as operating temperature data.The informing section 8 also acquires the operating time data indicatingthe operating time from a timer included in the informing section 8 or atimer of the temperature controller 16. The informing section 8 thenconverts this data to the operating time at 1200° C. and integrates theconverted values. When an integration value exceeds a predeterminedintegration threshold value, the informing section 8 transmits themaintenance information, such as the warning indicating the replacementtiming for the conductor tube 11. Functions of the informing section 8other than the above are the same as those in the foregoing embodiment.In addition to the configuration illustrated in FIG. 4, the informingsection 8 may also be disposed on a side of the first superheated steamgeneration section 10A so as to transmit the maintenance informationindicating the replacement timing for the conductor tube 2 in the samemanner as in the foregoing embodiment.

It will be understood that the present invention is not limited to theabove-described embodiments, and various modifications may be madewithout departing from the spirit and scope of the present invention.

DESCRIPTION OF THE REFERENCE CHARACTERS

-   -   100 superheated steam generator    -   10 superheated steam generation section    -   2 conductor tube    -   8 informing section

What is claimed is:
 1. A superheated steam generator, comprising: aninduction heating type or electrically heating type superheated steamgeneration section configured to generate superheated steam by heatingsteam; and an informing section configured to transmit maintenanceinformation by employing, as a parameter, an operating temperature ofthe superheated steam generation section and an operating time at theoperating temperature.
 2. The superheated steam generator according toclaim 1, wherein the informing section acquires operating temperaturedata indicating the operating temperature of the superheated steamgeneration section, and operating time data indicating the operatingtime at the operating temperature, the informing section converts theoperating time to an operating time at a predetermined temperature andintegrates converted values, and the informing section transmits themaintenance information when an integration value exceeds apredetermined integration threshold value.
 3. The superheated steamgenerator according to claim 2, wherein the informing section correctsthe integration value on a basis of an amount of superheated steamgeneration in the superheated steam generation section, and theinforming section transmits the maintenance information when a correctedintegration value exceeds the integration threshold value.
 4. Thesuperheated steam generator according to claim 2, wherein the informingsection is configured to convert to an operating time at 1200° C. andintegrate the converted values.
 5. The superheated steam generatoraccording to claim 1, wherein the superheated steam generation sectioncomprises a conductor tube that permits passage of the superheatedsteam, and the informing section is configured to transmit themaintenance information indicating a replacement timing for theconductor tube.
 6. The superheated steam generator according to claim 5,wherein the informing section is configured to transmit the maintenanceinformation by employing, as a parameter, an operating time at anoperating temperature at which a volume reduction rate of the conductortube reaches or exceeds a predetermined value by operating for apredetermined period of time.
 7. The superheated steam generatoraccording to claim 1, wherein the informing section specifies atemperature range used for the maintenance information at the operatingtemperatures of the superheated steam generation section, and utilizesthe operating time at the operating temperatures included in thetemperature range, as the operating time at a highest temperature in thetemperature range.
 8. The superheated steam generator according to claim1, wherein the superheated steam generation section comprises: a firstsuperheated steam generation section of the induction heating typeconfigured to carry out induction heating by using, as a secondary coil,a first conductor tube that permits passage of steam, and a secondsuperheated steam generation section of the electrically heating typeconfigured to further heat superheated steam generated in the firstsuperheated steam generation section by electrically heating a secondconductor tube that permits passage of the superheated steam.
 9. Thesuperheated steam generator according to claim 8, wherein the informingsection is configured to transmit the maintenance information indicatinga replacement timing for the second conductor tube.
 10. The superheatedsteam generator according to claim 8, wherein the first superheated stemgeneration section generates superheated steam at less than 1000° C.,and the second superheated stem generation section generates superheatedsteam at 1000° C. or above.
 11. A maintenance method for a superheatedsteam generator of an induction heating type or an electrically heatingtype configured to generate superheated steam by heating steam, themaintenance method comprising: transmitting maintenance information byemploying, as a parameter, an operating temperature of the superheatedsteam generation section and an operating time at the operatingtemperature.